1. Field of the Invention
The present invention relates to a recording apparatus for forming images and characters by irradiating a light beam onto a recording medium that is fitted to a rotating recording drum and, more particularly, a recording apparatus that has the good recording property of a fine line without reduction in concentration and does not waste a recording energy.
2. Description of the Related Art
In recent years, there is employed a system that forms an image on a printing sheet by thermally transferring heat-sensitive material onto an image receiving sheet in response to image information by using a recording apparatus, which employs a recording head such as a laser light source, etc., and then passing the image receiving sheet and the printing sheet, superposed on this image receiving sheet, through an image transferring device to transfer the image formed on the image receiving sheet onto the printing sheet.
Meanwhile, the laser recording head employed in the recording apparatus of this type in the prior art to have the light intensity distribution of the light beam having the Gaussian profile as shown in FIG. 4 is employed. In other words, assume that the X-axis is a sub-scanning direction, the Y-axis is a main scanning direction, and the Z-axis is the light intensity (mW/μm2) in FIG. 4, the light intensity becomes maximum at a location where the X-axis is 0 and the Y-axis is 0 and then the light intensity is reduced as the position goes far from the location where the X-axis is 0 and the Y-axis is 0.
Accordingly, if this light intensity in the main scanning direction is integrated every sub-scanning direction, integral values of the light intensity exhibit the Gaussian profile as shown in FIG. 5. In FIG. 5, assume that the abscissa is the sub-scanning direction and the ordinate is the integral value (mW/μm) of the light intensity in the main scanning direction, the light intensity at the location where the X-axis is 0 is 18 (mW/μm) at a maximum, and then the light intensity is reduced as the position goes far from the location where the X-axis is 0 on positive/negative directions and then becomes close to 0 at locations of ±8 μm.
By the way, since a thickness of the line, which is recorded at a predetermined velocity by the light beam in FIG. 4, is determined as a range where the integral value of the light intensity in the main scanning direction is equal to or more than 9 mW/μm as shown in FIG. 6, a line width is in the range of ±2.8 μm from the location where the X-axis is 0, i.e., a diameter is about 5.6 μm.
Therefore, for example, if the power of the light beam is varied to increase by 10%, the range is varied as shown in FIG. 7. That is, the line width is determined with the range where the integral value of the light intensity in the main scanning direction is in the range of more than 9 mW/μm, the line width is in the range of ±3.05 μm from the location where the X-axis is 0, i.e., the diameter is about 6.1 μm. That is, the line width is increased by about 10 from 5.6 μm in FIG. 6 to 6.1 μm in FIG. 7.
Also, if either humidity is reduced by about 20% or a recording velocity is increased by about 20%, the sensitivity is lowered by almost 10%. Thus, since the integral value of the recorded light intensity in the main scanning direction is in the range of more than almost 10 mW/μm as shown in FIG. 8, the line width becomes about 5.3 μm. That is, the line width is reduced by about 5% from 5.6 μm in FIG. 6 to 5.3 μm in FIG. 8. In this manner, it was found that, if the recording is carried out by the light beam having the Gaussian profile in the prior art, the line width is changed due to various factors. If so, it is impossible to get the predetermined concentration stably when external and internal noises (error factors) are present.